Normally curved flexible resilient drill guide and method for producing the same



April 19, 1955 UBLIN ATTORNEYS NORMALLY CURVED FLEXIBLE RESILIENT DRILL GUIDE AND METHOD FOR PRO- DUCING THE SAME John A. Zublin, Los Angcles, Calif.

Application ()ctober 3, 1951, Serial No. 249,533

6 Claims. (Cl. 255--1.6)

This invention relates to a normally curved, flexible, resilient drill guide for use in drilling lateral bores deviating from existing vertical well bores and to a method for producing the same. Normally curved, flexible, resilient drill guides capable of employment in the drilling of deviating bores from existing vertical well bores are not, per se, new. Such resilient curved guides are generally employed in drilling operations with a flexible torque transmitting member extending through the guide and interconnecting the drill bit and the lower end of the drill string so that rotation of the drill bit may be produced by rotating the drill string extending to the top of the well above the curved guide. Thus, the normally curved resilient guide functions to guide the drill bit laterally into the wall of the well bore to produce, upon bit rotation, a bore deviating from the existing well bore. Also, such flexible resilient curved guides have been employed in the drilling of deviating well bores where such guide is connected between the lower end of the drill string and a turbine drill bit, the driving power for the drill bit in this case being supplied by drilling fluid fed to the turbine bit through the drill string and curved guide.

In the method of producing the prior art normally curved, flexible, resilent drill guides, a straight, unslotted section of steel tubing has been bent to the desired normal curvature of the drill guide and heat treated to set the same with approximately spring steel resiliency in the curved configuration. Thereafter the helical slot requisite to impart resiliency in the normally curved drill guide has been cut by a suitable cutting torch. The cutting of the slot has had to be accompanied by concurrent cooling to prevent loss of the temper in the guide. Drill guides produced pursuant to this prior art practice have been provided with a spiral or helically extending slot which, in the normally curved, unstressed configuration-of the drill guide, is of the same width throughout its length and thus the normally curved, flexible, resilient drill guide is capable of flexing either to a curvature of lesser radius that that of its normally unstressed configuration or to a curvature of greater radius than that of its normally unstressed configuration.

I have now found that it is highly important to provide a normally curved, flexible, resilient drill guide having a predetermined minimum radius of curvature in its normally curved, unstressed configuration and which is therefore capable of flexing only to a curvature of greater radius and incapable of flexing to a curvature of lesser radius than the radius of curvature occupied thereby in its normally unstressed configuration.

The present invention has as its purpose and object the provision of a normally curved, flexible, resilient drill guide which, in its normally unstressed, curved configuration, has the minimum radius of curvature to which it is capable of being flexed and which can be flexed only to a curvature of greater radius than that of its normally unstressed configuration. It is also the purpose and object of the present invention to provide a method for producing such an improved, normally curved, flexible, resilient drill guide which obviates the necessity of the complicated and costly operation of bending an unslotted pipe section of large diameter and substantial wall thickness and of cooling the same during the cutting of the slot whereby loss of temper occurs.

Further and more detailed objects of the invention will 2,766,615 Patented Apr. 19, 1955 ice become apparent as the description proceeds which will be given in connection with the accompanying drawings wherein:

Figure 1 is a view in side elevation of a seamless steel pipe section in which a spiral slot of equal width throughout its length has been cut;

Figure 2 is a view in side elevation showing the position of the spirally slotted drill pipe section on a mandrel for the heat treating and quenching operation;

Figure 3 is a view in side elevation of a completed normally curved, flexible, resilient drill guide conforming to the invention;

Figure 4 is a detailed, fragmentary view showing the nature of the slot that is cut in the straight seamless tube of Figure l, and

Figure 5 is a detailed, fragmentary view showing the deformed nature of the slot as it exists in the finally produced, flexible, resilient drill guide illustrated in Figure 3.

In practicing the method of the present invention to produce a normally curved, flexible, resilient drill guide having its minimum radius of curvature in its normally unstressed configuration, the first step resides in cutting a generally helical or spiral slot 10 in the straight, seamless, alloy steel tube 11. Alloy tubing appropriate for use in practicing the method is of SAE 4135 to SAE 4139. Conventionally, the slot is usually started by cutting a small hole 12 near one end of the straight tube. The slot is cut by a suitable torch of the oxy-acetylene type and terminates near the opposite end of the tube 11 in the small opening 13 similar to the hole 12. The pitch of the slot 10 is preferably about twice the diameter of the pipe section 11. In other words, for a pipe section of four and one-half inches 0. D. the pitch of the slot 10 will be about nine inches. Where a radius of curvature for the normally curved, flexible, resilient drill guide of about 16 feet in its unstressed configuration is desired, the width of the slot may be in the neighborhood of three thirty-seconds of an inch. As will be observed by reference to Figure 4, the cutting of the slot 10 is so controlled as to produce intermeshing dovetailed teeth 14 and 15 which act in this instance in the same manner as more fully detailed in my prior Patent 2,515,365. Additionally, by reference to Figure 4, it will be observed that the slot 10 has a uniform width a throughout its length when initially cut in the straight, seamless pipe section 11.

The straight pipe section 11, after having the slot 10 of uniform width throughout its length cut therein as indicated in Figures 1 and 4, is next forced onto the curved mandrel 16 which has a predetermined radius of curvature corresponding to the desired normal radius of curvature in unstressed configuration of the normally curved, flexible, resilient drill guide to be produced.

The action of forcing the helically slotted, straight, seamless tube 11 onto the curved mandrel 16 results in a substantially complete closing of the slot 10 as indicated at 17 (Figure 5) on that side of the pipe section 11 of minimum radius and a corresponding substantially complete opening of the slot 10 as indicated at 18 (Figure 5) on that side of the pipe section 11 having the greatest radius when the pipe section is held on the mandrel 16. The ends 19 and 20 of the mandrel 16 are next preferably welded, though they may be otherwise fixedly secured to the bar 21 which prevents the assembly as shown in Figure 2 from changing its configuration or shape when subjected to the requisite high temperature of the heat treating step.

After the helically slotted tube 11 has been placed on the mandrel 16 and the fixed assembly of Figure 2 made up, that entire assembly is subjected to an appropriate heat treating step to give the seamless tube the necessary hardness which may be accomplished in a suitable oil, gas or electric furnace. The heat treating is so controlled that upon subsequent quenching the seamless, slotted, alloy tube will have approximately spring steel characteristics.

By way of example, the heat treating step may be effected by subjecting the assembly of Figure 2 to a temperature of approximately 1600 F. for a time period of about four hours.

Upon completion of the heat treating step, the assembly of Figure 2 is next quenched by a more or less conventional quenching operation which may, by way of example, be accomplished by removing the assembly from the furnace, quenching the same in oil, followed by placing the assembly back in the furnace where it is drawn at a temperature of about 990 F. for about eight hours then removed and slowly cooled in a warm room. This procedure imparts a Rockwell C hardness to the finished pipe of 4244.

Subsequent to the quenching step, the bar 21 is cut away from the mandrel 16 and the now permanently set, normally curved, flexible, resilient drill guide is slipped off the mandrel l6 and will thereafter retain the same fixed predetermined radius of curvature in its normally unstressed configuration in which form it is illustrated in Figure 3. In this form the slot 1% along the line 2 2' of minimum radius is substantially completely closed, whereas the slot 10 along the line 23 of maximum radius of the drill guide in its unstressed configuration is sub stantially completely open.

It will thus be appreciated that in final form the normally curved, flexible, resilient drill guide of the present invention is incapable of flexing to any substantial extent to a curvature of lesser radius than that of its normally unstressed configuration but that it is capable of flexing to a curvature of greater radius within the limits of the dimensions of the slot 10.

In the unstressed, normally curved configuration of the drill guide of the present invention the intermeshing teeth 14 and 15 will abut against each other as indicated at P in Figure 5 and restrict flexing of the drill guide to a lesser curvature but will freely permit flexing thereof to a greater curvature.

By this structure of drill guide the imposition of excess weight on bit at the surface of the well will not occasion any buckling of the drill guide.

it will be observed that through the practice of the method herein disclosed slotting of the pipe is effected while the same is in straight form. It is much easier to uniformly slot the pipe in straight form and prior to tempering than it is to slot the pipe in its curved form.

It will be appreciated that a straight pipe section can be slotted in an appropriate cutting machine by merely rolling the straight pipe, Whereas with a curved pipe such an operation is impossible.

Having thus disclosed my invention, what I claim is:

1. A method of producing a normally curved flexible resilient drill guide for use in drilling lateral bores deviating from existing vertical well bores comprising initially cutting in a straight steel pipe of predetermined length a generally spiral slot of equal width throughout its length, forcing the straight spirally slotted pipe upon a curved rigid mandrel of predetermined radius to effect substantial closing of said slot on the side of the mandrel of minimum radius and substantial opening of said slot on the side of the mandrel of maximum radius, heat treating said spirally slotted steel pipe while held on said curved rigid mandrel, quenching the heated slotted pipe to approximately spring steel characteristics and thereafter removing said slotted pipe from said mandrel.

2. A method of producing a normally curved'flexible resilient drill guide for use in drillin lateral bores deviating from existing vertical well bores comprising initially cutting in a straight steel pipe of predetermined length a generally spiral slot of equal width throughout its length, so controlling the cutting of the slot as to provide intermeshing dovetailed teeth along the same, forcing the straight spirally slotted pipe upon a curved rigid mandrel of predetermined radius to effect substantial closing of said slot on the side of the mandrel of minimum radius and substantial opening of said slot on the side of the mandrel or" maximum radius, heat treating said spirally slotted steel pipe while held on said curved rigid mandrel, quenching the heated slotted pipe to approximately spring steel characteristics and thereafter removing said slotted pipe from said mandrel.

3. A method of producing a normally curved flexible resilient drill guide for use in drilling lateral bores deviating from existing vertical well bores comprising initially cutting in a straight steel pipe of predetermined length a generally spiral slot of equal width throughout its length, so controlling the cutting of the slot that it has a pitch approximately twice the outside diameter of the pipe, forcing the straight spirally slotted pipe upon a curved rigid mandrel of predetermined radius to effect substantial closing of said slot on the side of the mandrel of minimum radius and substantial opening of said slot on the side of the mandrel of maximum radius, heat treating said spirally slotted steel pipe while held on said curved rigid mandrel, quenching the heated slotted pipe to approximately spring steel resiliency and thereafter removing said slotted pipe from said mandrel.

4. A method of producing a normally curved flexible resilient drill guide for use in drilling lateral bores deviating from existing vertical well bores comprising initially cutting in' a straight steel pipe of predetermined length a generally spiral slot of equal Width throughout its length, so controlling the cutting of the slot that it has a pitch of approximately twice the outside diameter of the pipe and is provided with intermeshing dovetailed teeth along the same, forcing the straight spirally slotted pipe upon a curved rigid mandrel of predetermined radius to effect substantial closing of said slot on the side of the mandrel of minimum radius and substantial opening of said slot on the side of the mandrel of maximum radius, heat rearing said spirally slotted steel pipe while held on said curved rigid mandrel, quenching the heated slotted pipe to approximately spring steel resiliency and thereafter removing said slotted pipe from said mandrel.

5. A normally curved flexible resilient drill guide for use in drilling lateral bores deviating from existing vertical well bores comprising a normally curved steel tube heat treated to retain such curved configuration and resiliently resist, deflecting forces tending to deform said tube from such curved configuration, said tube having a generally helical slot in the tube wall extending substantially from end to end thereof, said slot deviating from a true helical path to provide along the sides of said slot intermeshing dovetailed teeth to limit the extent of opening of said slot, said slot being substantially closed on the side of said tube of the smallest radius and substantially open on the side of said tube of the greatest radius whereby said tube is precluded from flexing to a radius of curvature smaller than its normal unstressed curvature but is resiliently flexible toward a straight configuration.

6. A normally curved flexible drill guide as recited in claim 5 wherein the pitch of the helical slot is approximately twice the outside diameter of said normally curved steel tube.

References Cited in the file of this patent UNtTED STATES PATENTS 1,451,936 Young Apr. 17, 1923 1,858,965 Nagamine May 17, 1932 2,022,532 Beans Nov. 26, 1935 2,218,864 'Widgren Oct. 22, 1940 2,336,338 Zublin Dec. 7, 1943 2,515,365 Zublin July 18, 1950 2,571,644 Zubl'm Oct. 16, 1951 FOREIGN PATENTS 576,402 Great Britain Apr. 2, 1946 

